Vehicular hydraulic lifts whether of single or two port constructions generally are installed below ground level and move vertically through supporting cylinders by means of an hydraulic system with the supporting bolsters pivotably supporting swing arms for engaging the undercarriage of a vehicle to be elevated. The vertically movable pistons are accurately machined and the cylinders are subjected to damage and corrosion by reason of their location in the path of mechanics working beneath the vehicle and drainage problems in the area of lift installation necessitating considerable maintenance.
Various single post and double post vehicular lifts are widely used including the type shown in U.S. Pat. No. 3,393,772 which relates to a single post lift elevatable from below ground level. A two-post hydraulic lift vertically movable from below the ground level is disclosed in U.S. Pat. No. 3,331,470. Single post and double post above-the-ground lifts have also been used but generally they are constructed with structural support columns having open rectangular cross-sectional configurations, and are generally rather massive units occupying substantial floor space. The synchronization systems employed are relatively complex and necessitate substantial maintenance as do the hydraulic cylinders since they are relatively unguarded or protected.
The present above-the-floor vehicle hydraulic lift is "free-standing" and has the advantages of utilizing standard cylindrical columns of large diameter, unfinished, low carbon steel pipe which eliminates costly machining and hardening operations common with many lift designs and the problems incident to welding of essential components to the fabricated structure. Of considerable advantage in the present construction using the hollow cylindrical cross-sectional area of the double post above-the-floor lift columns, the enclosed construction provides a suitable integral protected enclosure for the hydraulic drive and lifting cylinders which will be protected from damage whether from improperly loaded vehicles or from accidents caused by mechanics working on the vehicles. By isolating the hydraulic cylinders within the columns of the lift, in addition to removing them from danger in the working area and from under an elevated vehicle, the critically important hydraulic system remains protected at all times thereby extending the useful life of the lift and keeping it relatively maintenance free.
With the large scale conversion to smaller cars and front wheel drives, the above-the-floor lift of the present invention is well suited to accommodate the off-center eccentric loading of the smaller vehicles while at the same time being able to adapt readily to the front to rear eccentric loading encountered by front wheel drive vehicles, since the column's cylindrical cross-section has equal strength in all directions.
The utilization of large diameter columns permits the use of larger stabilizing contoured rollers for supporting the carriage or bolster lifting arm assembly thereby decreasing appreciably the stresses to which the column and the rollers may be subjected resulting in decreased wear and longer operating life for the lift.
The hydraulic drive system utilizes two hydraulic lifting cylinders driven by a standard hydraulic power unit with interconnecting fluid lines with each of the cylinders being positioned in one of the columns and the hydraulic cylinders are positively synchronized by reason of their inverted relationship each to the other permitting hydraulic fluid in the rod end of the drive cylinder to be displaced into the rod end of the slave or nondrive cylinder and vice versa, making them move in synchronization and in equal increments. The synchronization of the hydraulic lifting cylinders eliminates the necessity of tying the displacement of the two cylinders together with chain or cable mechanisms. The simplicity of the positive hydraulic synchronization reduces wear, breakage and stretch appreciably affording a positively synchronized drive that is relatively insensitive to malfunction since no moving parts associated with the drive train of the lift are housed in the base which connects and supports the two lift columns.
An automatic locking mechanism is provided which prevents the downward movement of a supported vehicle, in a fail safe condition, in the event that a chain or chain support member fails. Tripping or tilting of a vehicle on its side which may occur on many lifts is prevented since any obstruction to downward movement is sensed causing the lift to be disabled until a correction is made. A lock pawl mechanism that is spring loaded will enable the lift arms and bolster to be lowered in increments under manual control with a chain-sensing mechanism that will override the manual control in the event a slack chain is detected in either column of the lift.
Therefore, an objective of the present invention is to provide an above-the-floor free-standing double column vehicular hydraulic lift in which the hydraulic system is enclosed within the columns of the lift to protect the hydraulic system and provide a compact drive-through vehicle lift.
Another objective of the present invention is to provide an above-the-floor hydraulic lift in which large diameter pipe may be utilized without costly machining and welding or hardening to provide a highly stable vehicle lift in which the lifting mechanism is hydraulically synchronized without moving mechanical parts and minimal rotation of the bolsters is encountered.
Yet a further objective of the present invention is to provide and above-the-floor hydraulic lift with an automatic locking system for maintaining the vehicle at a selected elevation and to lower the lift in increments that will be manually controlled but subjected to a sensing mechanism for detecting improper conditions precluding further manual operation until rectification of the problem detected.
Other objectives and many of the attendant advantages of this invention will become more readily apparent to those skilled in the hydraulic lift art and from the following detailed description of a preferred embodiment taking in conjunction with the accompanying claims which are not intended in any limitative sense and equivalents are intended.